This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-311019, filed Oct. 11, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to an information recording technique and particularly relates to a high density magnetic recording medium consisting of a novel information recording layer having a very small magnetic domain structure and realizing high recording resolution.
In recent years, the research and development of means for recording an enormous quantity of information have been actively underway. Among these means, the a real recording density of a magnetic recording medium employed for a computer hard disk apparatus has become higher with great strides.
At present, a recording system, which is referred to as xe2x80x9clongitudinal magnetic recordingxe2x80x9d, for recording signals with a magnetization vector oriented toward the in-plane direction of a recording film has been employed as a magnetic recording medium technique for a recording medium of this type. Further, attention is being paid to xe2x80x9cPerpendicular Magnetic Recordingxe2x80x9d (S. Iwasaki and Y. Nakamura; IEEE Trans. Magn., vol. MAG-13, pp. 1272-1277, 1977) for recording signals with a magnetization vector oriented toward the perpendicular direction of a recording film, as a method for realizing higher density recording.
Meanwhile, Coxe2x80x94Cr-based alloys have been mainly used as magnetic recording materials for recording layers according to any recording systems. The crystal orientation of a Coxe2x80x94Cr-based alloy provided right on an underlayer can be controlled according to the material, crystal orientation or lattice constant of the underlayer. It is, therefore, possible to control the direction of an easy axis of magnetization determining the direction of a magnetization vector. Currently, the research and development of longitudinal recording media and perpendicular recording media each using a Coxe2x80x94Cr-base alloy thin film made by the above method as an information recording layer is actively underway.
By contrast to the information recording medium using the Coxe2x80x94Cr-based alloy thin film stated above, Japanese Patent No. 3010156 teaches the structure of a perpendicular magnetic recording medium using a thin film of ordered alloy with L10 crystal structure having excellent thermal stability and high magnetocrystalline anisotropy, as shown in FIG. 12A, as well as a manufacturing method therefor. The perpendicular magnetic recording medium manufactured according to this manufacturing method is an information recording medium wherein an underlayer 40 mainly consisting of an element selected from Cr, Pt, Pd, Au, Fe, Ni, MgO and NiO and a compound thereof is employed and a thin film of ordered alloy with L10 crystal structure is used as an information recording layer 12 (the medium having the structure shown in FIG. 12A will be referred to as xe2x80x9csingle-layer perpendicular magnetic recording mediumxe2x80x9d hereinafter).
Further, the perpendicular magnetic recording medium is an information recording medium wherein a layer 30 (FIG. 12B) consisting of a soft-magnetic material such as Fe, FeSi alloy or Permalloy is provided and a thin film of ordered alloy with L10 crystal structure is used as the information recording layer 12 (the medium having the structure shown in FIG. 12B will be referred to as xe2x80x9cdouble-layered perpendicular magnetic recording mediumxe2x80x9d hereinafter).
Also, Japanese Patent Application No. 11-276414 proposes the structure of a perpendicular magnetic recording medium employing a thin film of ordered alloy with L10 crystal structure realizing high signal output and high recording resolution and having high magnetocrystalline anisotropy as shown in FIG. 12C and a manufacturing method therefor.
In case of the perpendicular magnetic recording medium using a thin film of ordered alloy with L10 crystal structure as stated above, however, it is not easy to control the magnetic characteristics of the thin film of ordered alloy with L10 crystal structure or, to be specific, the coercivity, saturation magnetization and magnetic domain size of the thin film. To improve the recording resolution of the recording medium and reduce medium noise for improving a signal to noise ratio, in particular, a technique for controlling the microstructure of the thin film of ordered alloy with L10 crystal structure and for reducing magnetic domain size is required.
Meanwhile, K. R. Coffer, M. A. Parker and J. K. Howard (IEEE Trans. Mag., vol. 31, pp. 2737-2739 (1995)) proposes a method for manufacturing a thin film of a composite obtained by adding ZrOX to a thin film of ordered alloy with L10 crystal structure and for controlling the microstructure of the thin film of ordered alloy with L10 crystal structure. With the technique proposed therein, the crystal orientation of an ordered phase with L10 crystal structure is not controlled, with the result that an obtained perpendicular magnetic component is small, making it difficult to use the perpendicular magnetic component for the perpendicular magnetic recording system suited for high density recording. Further, since annealing is performed after forming the composite thin film so as to form an ordered phase with L10 crystal structure exhibiting high magnetocrystalline anisotropy, this method requires a complicated medium manufacturing step.
As additives used for a composite thin film consisting of ordered alloy with L10 crystal structure, TaN (e.g., T. Shimatsu, E. G. Keim, T. Bolhuis, and J. C. Lodder; J. Magn. Soc. Jpn., S2-21, pp. 313-316 (1997)), Ag (e.g., S. Stavroyiannis, I. Panagiotopoulous, D. Niarchos, J. A. Christodoulides, Y. Zhang, and G. C. Hadjipanayis; Appl. Phys. Lett., 73, pp. 3453-3455 (1988)), C (e.g., M. Yu, Y. Liu, A. Moser, D. Weller, and D. J. Sellmyer; Appl. Phys. Lett., 75, pp. 3992-3994 (1999)), B (e.g., N. Li, and B. M. Lairson; IEEE Tran. Magn. vol. 35, pp. 1077-1081 (1999)), SiO2 (e.g., C. Chen, O. Kitakami, S. Okamoto, Y. Shimada, K. Shibata, and M. Tanaka; IEEE Trans. Magn., vol. 35, pp. 3466-3468 (1999)), Al2O3 (e.g., M. Watanabe, T. Masumoto, D. H. Ping, and K. Hono; Appl. Phys. Lett., 76, pp. 3971-3973 (2000)) and the like have been reported.
However, in case of a composite thin film consisting of ordered alloy with L10 crystal structure to which any one of the above additives is added, the crystal orientation of an ordered phase with L10 crystal structure is not controlled. Due to this, an obtained perpendicular magnetization component is small or an in-plane magnetization component is large, making it difficult to use such a composite thin film for the perpendicular magnetic recording system suited for high density recording.
That is, as for the thin film of ordered alloy with L10 crystal structure, an additive select guideline appropriate for a perpendicular magnetic recording medium, i.e., appropriate for controlling the crystal orientation of an ordered phase with L10 crystal structure and forming the ordered phase with L10 crystal structure has not been clarified so far.
Under these circumstances, demand for proposing a new composite thin film of ordered alloy with L10 crystal structure for a perpendicular magnetic recording medium is rising.
It is, therefore, an object of the present invention to provide a magnetic recording medium which is a perpendicular magnetic recording medium using a new composite thin film of ordered alloy with L10 crystal structure having high magnetocrystalline anisotropy, which can control the magnetic characteristic of an information recording layer or particularly reduce a magnetic domain size and which can ensure high density recording.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.
The present invention has been made in view of the above circumstances. To solve the above disadvantages and to attain the object, the following measures are taken according to the present invention. Namely, the inventor of the present invention discovered a novel composite thin film composition and finally completed the present invention based on this understanding.
That is, as a first embodiment of the present invention, a perpendicular magnetic recording medium, consisting of a composite thin film of a novel ordered alloy of L10 crystal structure so as to control the magnetic characteristic of an information recording layer or particularly to reduce a magnetic domain size, is proposed by a method described in claims.
[1] A magnetic recording medium having an information recording layer and capable of recording and reproducing information using a magnetic field, characterized by consisting of a composite of an ordered alloy of L10 crystal structure selected from a group A (: an FePt ordered alloy, a CoPt ordered alloy, an FePd ordered alloy and an alloy thereof), and MgO is proposed.
[2] A magnetic recording medium recited in [1], characterized in that on the information recording layer consisting of the composite, a Miller index (001) of a crystal lattice face of an ordered phase of L10 crystal structure consisting of the ordered alloy of L10 crystal structure is formed to be parallel to a surface of the information recording layer.
Further, [3] A magnetic recording medium characterized by having a layer structure having a layer consisting of a predetermined soft-magnetic material, a layer consisting of a predetermined nonmagnetic material and the above mentioned information recording layer formed sequentially in this order. In addition, [4] A magnetic recording medium recited in [3], characterized in that the nonmagnetic material is MgO. Moreover, [5] A magnetic recording medium recited in [3], characterized in that the soft-magnetic material is selected from a group B (: Fe, an Fexe2x80x94Si alloy and an Nixe2x80x94Fe alloy).